Today, insulating glass units have achieved widespread use as building components. In order to produce insulating glass units inexpensively and in high volume, modern manufacturing of insulating glass units is often mechanized and/or automated. Various materials may be used to manufacture insulating glass units, including sheets of glass, spacer frames, and various sealants. Insulating glass units may also include muntin bars. Muntin bars may be used for both functional and decorative purposes with glass windows or doors. The muntin bars are particularly useful when they retain their geometric configuration and do not separate, as well as when they are able to remain in a flat mating surface relation with the glass.